Watercraft



y 1952' B. K. L..ALMQVIST ET AL 2,597,048

WATERCRAFT Filed Dec. 28, 1948 FIG]. E

Patented May 20, 1952 Olof Elgstriim, -Alvsjo, "Sweden, assignors toAktiebolaget Supermarin, Stockholm, Sweden,

a corporation of Sweden Application December 28, 1948, Serial No. 67,602In Sweden May 24, 194 8 3 Claims. (01. iii-6.6.50

This invention relates to hydrodynamically supported watercraft in-whichthe hull at normal speed rises entirely clear of the water. Morespecifically, the invention relates to such Watercraft in which thesubstantial part of the craft is supported by one or more hydrodynamicalsustainers, while the remaining weight is supported by a. forwardlyplaced planing surface or surfaces adapted at normal speed to rest onthe surface of the water even if the water surface is disturbed bywaves, for the purpose serving as a stabilizer.

One object of the invention is to construct the stabilizer so that thesame has both a.- longitudinal and a latitudinal stabilizing effect onthe hull.

Further objects of the invention will be better understood from thedescription hereinbelow, by reference to the annexed drawings which showembodiments of the device according to the invention.

Fig. 1 is a side elevation illustrating the hull of a watercraft with ahydrofoil and a forward stabilizer attached thereto and showing the hullsupported clear of the surface of the water.

Fig. 2 shows in the same manner as Fig. 1 a watercraft having twohydrofoils attached thereto.

Fig. 3 showsthe hull of the watercraft according to Fig. 1 in top view.

Fig. 4' is a section taken on the line IVIV in Fig. 1.

Fig. 5 is a section taken on the line VV in Fig. 4.

Fig. 6 is a section taken on the line VIVI in Fig. 1.

Fig. 7 shows in the same way as Fig. 6. a modifi embodiment of thestabilizer.

Figs. 8, 9 and 1 0 are sections taken on the lines VIII-VIII, IX IX, andXX respectively in Fig. 6.

Fig. 11 is a diagrammatical section taken on the line IV-IV in Fig. 1illustrating the latitudinal stabilizing force of the hydrofoil. Thefull lines show the watercraft in normal position, while the dottedlines show the craft tilted by a foreign force.

Fig. 12 is a diagrammatical section taken on theline VIVI in Fig. 1illustrating the latitudinal stabilizing force of. the forwardstabilizer. The full lines show the watercraft in normal position, whilethe dotted linesshow the craft tilted by a foreign force.

In the. drawing l indicates the hull of a waterby G. A hydrofoil 3 forinstance of known type 2 is attached to the hull by means of supports 2.It will be seen from Fig. 5 that the lower face of the hydrofoil isplane and has an inclination 1) towards the horizontal plane of about 3.The hydrofoil is arranged behind the centre of gravity G.

At the forward part of the hull, preferably at the how, there isarranged a stabilizer a adapted at normal speed of the craft to restupon the surface of the water and thus hold the forward part of the hullclear of said surface, as shown in Figs. 1 and 6, the hydrofoil 3maintaining at the same time the aft part of the hull above the waterlevel. i

The stabilizer consists in the embodiment according to Figs. 1 and 6 ofa central portion forming two planing surf-aces 5 and 6, one at eachside of the hull. The forward edge of surfaces 5 and 6 is horizontal. Atthe outer end of each of; the horizontal parts 5 and 6 there is anupwardly inclined portion, 1 and 8 respectively, extending above thewater surface when the central portion of the stabilizer is restingthereon.

The two surfaces 5 and 6 are connected with each other and with the hullrespectively by means of upwardly and inwardly inclined plates l2extending longitudinally of the hull. The surfaces 5 and 6- are furtherconnected with the hull by means of supports 9 and ID.

As will be seen from Fig. 8, the parts 5 and 6 have a longitudinal crosssection of a shape similar to that of the hydrofoil. The parts 5 and 6,however, have preferably a longer extension in longitudinal direction ofthe hull than the hydrofoil 3. Moreover, the lower side of the parts 5and 6 facing the water, which side is plane or concave, has aninclination 1; towards the horizontal plane which is greater than 3,preferably about 5; The planing surface of the parts 5 and B have thusan angle of attack to the water which is greater than the angle ofattack to the water of the hydrofoil 3. The forward edge of the parts 5,6 is preferably sharp and the profile (Fig. 8-) is, as will be seen inthe drawing, of modified hydrofoil type.

Also the upwardly inclined lateral portions 1, 8 of the stabilizer havean inclination rearwards and downwards from their forward edge. Thisinclination 0 Fig. 9, is preferably greater than that of the parts 5, 6,for instance about 7. On the other hand, the plane lower sides of theparts I2 have no inclination in the longitudinal direction of the craft(Fig. 10)

Fig. '7 shows a modified embodiment of the stabilizer. The lateralportions ll, I8 thereof incline in this case in a curve upwards from thecentral surfaces of the stabilizer which latter also in this case have ahorizontal forward edge and slide on the water surface.

The stabilizer is preferably made of metal and thus does not have anyinnate buoyancy.

It will be understood that the parts 5, B may be made so as to extenduninterruptedly in transverse direction underneath the hull, whilaccording to other embodiments they may be divided into more than twoparts.

Fig. 2 shows a watercraft having two stabilizers 4 of the kind shown inFig. 1, the hull being provided with two hydrofoils 3. If desired, threeor more hydrofoils may be arranged. The dynamic sustaining systemcreated by the hydrofoils is located so that the upwardly directedresultant force R of said system is located aft of the centre of gravityG of the watercraft. One

or more of the hydrofoils 3' may be assumed to be of such a type as hasno latitudinal stabilizing force of its own.

The stabilizer or forward planing surface or system of surfaces, in thefollowing called foreplane, has five distinct functions when used on adynamically sustained watercraft.

(1) Automatic control of the angle of attack of the hydrofoil (dynamicsustaining systems): The action of the foreplane in planing on thesurface of the water in running position provides an automatic check onthe angle of attack to the water of the hydrofoil or hydrofoils, whichare fixed at a given angle to the hull-of the watercraft, in thefollowing manner: should the foreplane, for example, be lifted upwardsby the ction of a wave or some other similar surface irregularity in thewater, this upward movement of the foreplane is transferred to the bowof the hull and thence to the hydrofoil, causing an automatic increaseof the angle of attack to the water of the hydrofoil, simultaneouslyincreasing the lifting force on said hydrofoil and thereby raising thestern of the boat to a somewhat lesser degree than, but in directproportion to, the lift of the bow. The result is a decrease in thepitching motion characteristic of a displacement boat or a planing boatin disturbed water. (The same process in reverse naturally is the resultof a sudden drop in the foreplane resulting in a decrease in the angleof attack of the hydrofoil). (2) Shock absorbing effect in disturbedwater: The sharp profile and wing form of the foreplane, plus its lack,of innate buoyancy, enable it to proceed in a plane with the averagesurface of the water rather than with the constantly changing levels ofminor fluctuations in that surface caused by waves or other similardisturbances. The leading edge of the planing surface thus cuts throughthe tops of the smaller waves and gives the boat a smooth horizontalcourse. The entire structure of the foreplane is also a protectionagainst the bouncing or slapping so common in fast boats of the planingtype (i. e.: racing boats) operating in Water which is not perfectlycalm. If the bow of a dynamically sustained boat equipped with aforeplane should rise clear of the water just after a wave top, and thenfall toward the water surface in the following trough, the foreplanestructure provides a shock absorber for the hull; the resistance of theforeplane to vertical passage through the water being pronounced, butnot as great as the corresponding resistance of a displacement orplaning hull. The result in the case of the foreplane-equipped boat is abreaking of the impact 4 and a gradual braking of the fall a thecombined foil and planing eifects of the foreplane take effect andprevent more than a momentary contact of the hull itself with the waterbefore normal running position is resumed. The sharp jar whichaccompanies such a manoeuvre in a displacement or planing hull iseliminated.

(3) Function as a hydrofoil during the moment of lift: The hydrofoilprofile of the foreplane, acting under water before acceleration hasproceeded to the point where the actual hydrofoils or dynamic sustainershave enabled the hull to free itself from the surface, enables theforeplane to act at these low speeds as a dynamic sustainer in itselfand to contribute a strong lift of its own to the forward portion of theboat. By reason of the foreplanes greater surface area as compared tothe hydrofoils, this lift is more effective than that of the foils andthereby (see point 1) increases the angle of attack of the foils,simultaneously increasing their capacity for lift and freeing the entirehull sooner than would otherwise be the case. The action of theforeplane in rising quickly to the surface, even at low speeds, andbeginning to plane, raises the forward portion of the boat out of thewater, decreasing the total water resistance of the boat, enabling it toaccelerate faster, and thereby hastening the completion of the liftingprocess additionally.

(4) Longitudinal stabilizing function: The nature of a hydrofoiloperating entirely or partly under water is such that it has nostabilizing effect along the longitudinal axis of the boat to which itis attached and which it supports wholly or partially. In order toachieve such a longitudinal stability some means of orienting the boatsprogress to a plane of reference parallel with the plane of the waterssurface is necessary. This orientation is provided by the foreplane,which follows the water surface itself and prevents the boat, if theforeplane is placed according to the drawing with respect to the centerof gravity of the boat, from either nosing down or rearing on the water.

(5) Latitudinal stabilizing function; A bowed hydrofoil, such as thatshown in the drawing, provides a strong latitudinal stabilizing force ofits own, but this force does not take effect until tipping has reached apoint where the perpendicular joining the lines representing the weightof the watercraft at the center of gravity and the line representing thelift at the center of lift of the foil is sufiiciently large to producean effective stabilizing moment. (See Fig. 11.) This may not occurbefore a tilt of several degrees is achieved. The foreplane, however,provides an immediate latitudinal stabilizing force at the firstincidence of tilting. The upwardly inclined lateral portions 1, 8 of theforeplane-whose angle of attack to the water is greater than that of thenormal planing surfaces 5, 8are placed in contact with the water duringtilt and immediately provide a stabilizing force perpendicular to theirlower faces (see Fig. 12). The V-shaped gap formed by the plates l2 inthe central portion of the foreplane has the effect of quickly shiftingthe center of lift of the system further to the down side of the systemduring tilt, thus producing a rapid righting tendency.

The said function of the foreplane even if same is combined with ahydrofoil having a latitudinal stabilizing effect of its own, is ofspecial importance at relatively low speed of the craft, since thestabilizing tendency of the bowed hydrofoil does not reach its fullefiiciency before considerable running speed is reached, while thedescribed effects of the foreplane are pronounced even at low speeds.

It will be seen from the aforesaid that the mode of operation of thewatercraft, both when starting and during running in disturbed water, isattained by means of members (hydrofoil and a forwardly placedstabilizer) which are rigidly attached to the hull. Thus, movablemembers are superfluous. The combination of the forwardly placedstabilizer of the above-described construction with at least onehydrofoil having a latitudinal stabilizing force of its own will makethe watercraft insensitive to horizontal variations of the position ofthe centre of gravity arising through forward, aftward or lateraldisplacements of the watercrafts variable load.

As will be seen from the drawing the centre of gravity G of the craftitself including the machinery is situated at a relatively shortdistance forward of the upwardly directed resultant force of the dynamicsustaining system and at a considerable distance aft of the stabilizer.

What we claim is: l

1. In a dynamically supported watercraft with hull rising clear of thewater, a dynamic sustaining system comprising at least one hydrofoil andlocated such that the upwardly directed resultant force of said systemis located near to and aft of the center of gravity of the craft so asto carry the main portion of the weight of the craft, and a stabilizerspaced from the hull and located forwardly of the center of gravity at aconsiderably greater distance therefrom than said sustaining system soas to carry a small amount only of said weight, said stabilizer having acentral portion adapted at normal speed to rest on the surface of thewater, and lateral portions having upwardly inclined faces extendingabove the surface of the water when said central portion is restingthereon, the central portion of said stabilizer forming two planingsurfaces, one at each side of the longitudinal axis of the craft,inwardly and upwardly inclined plates extending longitudinally of thecraft and constructed and arranged to connect said planing surface toeach other.

2. In a dynamically supported watercraft with hull rising clear of thewater, a dynamic sustaining system comprising at least one hydrofoil andlocated such that the upwardly directed resultant force of said systemis located near to and aft of the center of gravity of the craft so asto carry the main portion of the weight of the craft, and a stabilizerspaced from the hull and located forwardly of the center of gravity at aconsiderably greater distance therefrom than said sustaining system soas to carry a small amount only of said weight, said stabilizer having acentral portion forming at least one planing face adapted at normalspeed to rest on the surface of the water, and lateral portions havingupwardly inclined faces extending above the water level when saidcentral portion is resting thereon, the angle of attack to the water ofsaid planing face being smaller than the angle of attack to the water ofsaid upwardly inclined portions.

3. In a dynamically supported watercraft with hull rising clear of thewater, a dynamic sustaining system comprising at least one hydrofoil andlocated such that the upwardly directed resultant force of said systemis located near to and aft of the center of gravity of the craft so asto carry the main portion of the weight of the craft, and a stabilizerspaced from the hull and. located forwardly of the center of gravity ata considerably greater distance therefrom than said sustaining system soas to carry a small amount only of said weight, said stabilizer having acentral portion adapted at normal speed to rest on the surface of thewater, and lateral portions having upwardly inclined faces extendingabove the surface of the water when said central portion is restingthereon, th central portion of said stabilizer forming two planingsurfaces, one at each side of the longitudinal axis of the craft,inwardly and upwardly inclined plates extending longitudinally of thecraft and constructed and arranged to connect said planing surfaces tothe body of the hull.

BO KARL LORITZ ALIVIQVIST. BJGRN OLOF ELGSTROM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,976,046 Tietjens Oct. 9, 19342,139,303 Grunberg Dec. 6, 1938 2,257,405 Von Burtenbach Sept. 30, 19412,257,406 Von Burtenbach Sept. 30, 1941 FOREIGN PATENTS Number CountryDate 517,518 Germany Feb. 4, 1931

